1. Field of the Invention
The present invention relates to a circuit for operating a microwave oven, and more particularly, to an inverter circuit which can operate a microwave oven by using a DC voltage.
2. Background of the Related Art
Recently, enhancement of an energy consumption efficiency and performance of most home appliances, such as electric rice cookers, air conditioners, refrigerators and the like, are sought by applying an inverter operating system thereto. It is because users' demand for home appliances that have a high energy consumption efficiency, an improved performance and convenience in use becomes the greater, as goods for convenience of life, such as the electric rice cookers, air conditioners, refrigerators and the like, are used the wider gradually.
Such an inverter operating system is applied to the microwave oven, too. The microwave oven heats an object by directing microwave generated from a current to the object. For generation of the microwave, an inverter operating system of control is employed.
FIG. 1 illustrates a related art circuit for operating a microwave oven.
Referring to FIG. 1, a related art inverter circuit for operating a microwave oven is provided with a rectifying circuit 15 for rectifying an AC current from an AC power source 10, which rectified current is provided to a primary side of a transformer through the inductor 20. There is a magnetron 40 on a secondary side of the transformer 25 for generating microwave. That is, the magnetron 40 is operative from the voltage induced at the secondary side of the transformer 25 for generating the microwave.
A primary side voltage of the transformer 25 is controlled by a power switching part 30. The power switching part 30 is turned on/off in response to a PWM control signal generated at an inverter operating part 55 based on an output control signal from the microcomputer 35, to control a primary supply voltage of the transformer 25.
A current to the magnetron 40 is detected at a current transformer 45, rectified at a rectifying circuit 50, and forwarded. A signal of a current intensity to the magnetron 40 detected at the current transformer 45 is provided to the microcomputer 35.
In the meantime, an anode of the magnetron 40 has no current, but a high voltage provided thereto from the transformer 25, until a heater in the magnetron 40 is heated enough to emit thermal electrons. This state is a non-oscillation region of the magnetron 40, and it takes a certain time period (about 2 seconds) until the heater in the magnetron 40 makes a regular emission of the thermal electrons enough to generate the microwave.
That is, only after the regular oscillation of the magnetron 40 is made by the heater, the current flow to the anode of the magnetron 40 starts. This current is called as an anode current, and a product of the anode current and an anode voltage is a power P provided to the magnetron 40. A product of the power P to an efficiency of the magnetron 40 represents an intensity of the microwave from the magnetron 40.
Therefore, the current intensity to the magnetron 40 is in correspondence to a microwave output, such that if the current intensity is high, the microwave output is high, and if the current intensity is low, the microwave output is low.
That is, the current intensity detected at the current transformer 45 is used for controlling the microwave output, as the current intensity is provided to the microcomputer 35 to control the current intensity to the magnetron 40.
However, the related art circuit for operating a microwave oven has the following problems.
Because the related art microwave oven is only operative on an utility AC power, operation of the magnetron in outdoor without the utility AC power is not possible, and operation of the magnetron is also not possible in a black out.